DE .FILE 84 - apps.dtic.mil · date of Sro.61Bao.39Nb206, the congruently melting composition.2...

2

*Th. 83-1299 SC5344.7FR

RESEARCH ON FERROELECTRIC MATERIALSFOR MILLIMETER WAVE APPLICATION

Final ReportFor Period August 5, 1981 through December 4, 1982

August 1983

00 DARPA Order No.: 4240Program Code: 1D10

Name of Contractor: Rockwell International CorporationEffective Date of Contract. August 5, 1981

V 4 Contract Expiration Date: August 4, 1982Amount of Contract Dollars: $379,182Contract Number: F49620-81-C-0090Principal Investigators: Dr. R.R. Neurgaonkar

(805) 498-4545, Ext. 109Dr. L.E. Cross

1m4 Pennsylvania State University(814) 865-1181

Dr. W.F. Hall(805) 498-4545 Ext. 189

Dr. W.W. Ho(805) 498-4545 Ext. 194

Sponsored by 'F

Defense Advanced Research Projects Agency (DoD) I - .

DARPA Order No. 4240

Monitored by AFOSR/NE Under Contract No. F49620-81-C-0090 JAN 2 3"A984

A

The views and conclusions contained in this document are those of the authors andshould not be interpreted as necessarily representing the official policies, eitherexpressed or implied, of the Defense Advanced Research Projects Agency or theUnited States Government.

Approved for public release; distribution unlimited.

DE .FILE COPY 84 i .~ J...

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TABLE OF CONTENTS

Page

1.0 SUMMARY ........................................................... 1

1.1 Technical Problem ............................................ 1

1.2 General Methodology ......................................... 21.3 Technical Results ............................................ 21.4 Implications for Further Research ............................ 3

2.0 TUNGSTEN BRONZE COMPOSITIONS ...................................... 4

2.1 Single Crystal Growth of Srl-xBaxNb2O6 Compositions........ 52.2 SBN:50 and SBN:60 Characterzition .................. 142.3 The Tungsten Bronze Pb K Nb206 System .............. 152/4 PKLN/PKBN Characteriza ............................ 17

3.0 HIGH FREQUENCY DIELECTRIC MEASUREMENTS ............................ 25

3.1 Measurements of dn/dE ........................................ 263.2 Dielectric Studies ........................................... 27

4.0 CONCLUSIONS ....................................................... 34

5.0 PUBLICATIONS AND PRESENTATIONS .................................... 355.1 Publications ................ . . . . . . . . . . . . . . . . 35

5.2 Presentations .................... ............................ 35

6.0 REFERENCES ................................................ ........ 36

LIST OF TABLES

Table Page

2.1 Classification of Tungsten Bronze Family ...................... 5

2.2 Growth of SBN Single Crystals ................................. 9

2.3 Physical Properties of SBN .................................... 15

2.4 Physical Constants for Modified PbNb206 ...................... 24

3.1 Variations of dn/dE with Frequency and AppliedVoltage for SBN:50 ............................................ 27

C5278A/lbs

SECURITY CLASSIFICATION OF THIS PAGE (When Os,Ente,**c Unclas'sifiedRt'PRT OCUMNTAION AGEREAD INSTRUCTIONSR•PORT DOCUMENTkTION PAGE BEFORE COMPLETING FORM

1. REPORT NUMBER 2. GOVT ACCESSION NO I. RECIPIENT'$ CATALOG NUMBER

AFOSR-TR- 3 - 12 99 T4. TITLE (wad Subtitle) S. TYPE OF REPORT & PERIOD COVERED

RESEARCH ON FERROELECTRIC MATERIALS FOR FINAL REPORTMILLIMETER WAVE APPLICATION 5 AUG 81 - 4 DEC 82

S. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(*) S. CONTRACT OR GRANT NUMBEW.)

R. R. Neurganokar F49620r-81-C-0090

S. PERFORMING ORGANIZATION NAM4E AND ADORESS SO. PROGRAM ELEMENT. PROJECT. TASK

AREA & WORK UNIT NUMBERS

Rockwell international Corporation'.., .. -1049 Camino Dos Rios P 0 Box 1085 ° a ' ....Thousand Oaks, CA 91360 2306/B2

11. CONTROLLING OFFICE NAME AND ADDRESS IL REPORT DATIE

Air Force Office of Scientific Research/NE August 1983Building #410 -1. NUMBER OF PAGES

Boling AFB, DC 20332- 39I. MONITORING AGENCY NAME A ADORESS(II different from Controlling Olice) IS. SECURITY CLASS. (of Ihis topot

Unclassified

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IS. DISTRIBUTION STATEMENT (of dile Rep rt)

Apprv.! for pul I a 'e? ease;d1styihttlea unlimited.

17. DISTRIBUTION STATEMENT (of le abstract entered in Block 20, I dilffrent from Report)

Ill. SUPPLEMENTARY NOTES

?S. KEY WORDS (Continue on everse'side It necessary and Identify by block number)

Tungsten bronze compositions, Millimeter wave materials,Ferroelectric materials, Strontium barium niobate

S0. ABSTRACT (Continue on revers side It necessary and Identity by block number)

OVER

DD , '.AN. 1473 EDITION Of I NOV5G IS OBSOLETE Unclassified

SECURIrY CLASsrI-ATION Or ?MIS AGE ! ,, be,& ltnr , ed

~J~AS~IEDAIOSR.Th. 3 1 2 9 9SECURITY C.ASSIFICATION O r THIS PAGCIIn Date En ,"o Unclassified

%f2 "' -" ' . . " " " . . . -""

Te largest and highest quality singl, crystals of the tunisten bronze familyferroelectric compositions of the strontium - barium nioba e family reported

Ito date were prepared by Czochralski growth techniques. Low frequency,dielectric properties show low loss and high permittivity as expected.jAccurate high frequency dielectric measurements for several compositions weremade in a waveguide geometry from 30 to 100 GHz and the electric fieldI sensitivity of the microwave refractive index, dn/dE, was evaluated by amodulation technique in the same waveguide geometry. Although high values of

dn/dE were observed, an unexpectedly high dielective loss, which does not fitaccepted models for dielectric properties, was observed. This fact, coupledwith a high sample-to-sample variability, suggests a commonly occuringextrinsic factor such as growth defects or sample impurities as the keyelement limiting the use of these materials for phase control applications in.millimeter wave radar systems. Similar dielectric measurements were made on avariety of ceramic ferroelectrics. In general the losses were substantiallyhigher in these materials - . ." " ... . ... -.

- . k- *

...- M-

. . . . .. . . . . . !4

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LIST OF TABLES

Table Page

3.2 Dielectric Properties of Two SBN:60 Samples Beforeand After Poling ........................................... 29

3.3 Dielectric Properties of Three Annealed SBN:60 Samples ........ 30

3.4 Dielectric Properties of High Purity SBN:60 Samples ........... 31

3.5 Summary of Measured Dielectric Properties of SingleCrystal Ti 2 ............................................ ...... 32

3.6 Dielectric Properties of Orthorhombic PKLN Samples ............ 33

LIST OF FIGURES

Figure Pg

2.1 Phase boundary and Curie temperatures vs compositionfor Sr. xBaxNb206 ................................ 7

2.2 SBN:50 single crystal grown along the (001) direction ......... 10

2.3 SBN:60 single crystal grown along the (001) direction ......... 11

2.4 Idealized form of SBN single crystals ......................... 12

2.5 Variation of lattice parameters for the Pbl.2xKxLaxNb206solid solution ................................................ 18

2.6 Dielectric constant vs temperature of Pbl_ 2xKxLaxNb2 06 ........ 19

2.7 Variation of the ferroelectric transition temperature forPbI2xKx~xNb2O6, M = La or B .................... ........ 20

2.8 Pbl. 2^K La Nb206 dielectric properties as a function ofsintering temperature ......................................... 23

AIR FORCEX OFFICE ')F SCIEnTIFICFJL."" ] . NOTICE OF IRN : r. TO DTTC

, ,.g.. nrvuti,):' '1hi3 technl."-'n<,t i

#NBPECrTED MATTHEW J. KEK7,RChief, Teohnical Information DiviSiom

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1.0 SUMMARY

This technical report presents the results of the final three months of

a research program on ferroelectric materials for phase control applications in

millimeter wave radar systems. Originally a one-year program, this effort was

extended to fifteen months to take advantage of materials development activities

in related programs. The major accomplishments in the current period include

measurements of the electric field sensitivity of the microwave refractive index

in strontium barium niobate single crystals, and development of growth tech-

niques for Sro. 5Bao. 5Nb206 (SBN:50) single crystals of diameter exceeding 2 cm.

1.1 Technical Problem

On the basis of current models for ferroelectric materials, one pre-

dicts that certain ferroelectrics having a high dc permittivity £(o) should also

show high sensitivity of their microwave refractive index, n = /cJ-) to an ap-

plied electric field for microwave frequencies up to several hundred GHz. A low

absorptive loss is also predicted over the same range of frequencies. However,

the millimeter wave dielectric properties of these materials are largely un-

known, and growth of the most promising ferroelectrics in single crystal form is

generally difficult.

The present program was conceived on the basis of successful growth at

Rockwell of one such ferroelectric, Sro.61Bao.39Nb206 (SBN:60), and measurement

in this material of a substantial electric field sensitivity, dn/dE, of 10-6

meters/volt at 58 GHz. I With about an order of magnitude larger sensitivity,

one can design microwave components operating at practical control voltages

(under 200 volts) for phase shifting, modulation and switching. One attractive

concept is a planar dielectric lens for electronically steering a millimeter

wave radar beam, which could be used in high speed seeker applications.

The technical objective of the current study is to explore the range of

dielectric properties (primarily dn/dE and dielectric loss) achievable within

the SBN family. Other promising ferroelectrics are to be examined depending on

availability.

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1.2 General Methodology

There is an on-going program in development of growth techniques for

tungsten-bronze materials at Rockwell, which provides the principal source for

the Srl.xBaxNb206 ferroelectrics studied under the present contract. This

program has produced the largest and highest quality single crystals reported to

date of Sro.61Bao. 39Nb206 , the congruently melting composition. 2 Having these

crystals available as seeds greatly facilitates the Czochralski growth of other

SBN compositions and certain other tungsten bronzes. Also, through the ferro-

electrics program at Penn State University, a wide variety of other materials

have been made available for this study. These include ferroelectric and anti-

ferroelectric ceramics, as well as single crystals, many of which have been well

characterized by piezoelectric and low frequency dielectric measurement

techniques.

Accurate high frequency dielectric measurements on the selected system

have been carried out in a waveguide from 30 to 100 GHz.3 Power reflection and

transmission coefficients were determined on samples cut to fill the guide, and

sample dielectric properties were fitted to these observations. The electric

field sensitivity of the microwave refractive index, dn/dE, was evaluated by a

modulation technique in the same waveguide geometry.

1.3 Technical Results

During the first six months of this program, millimeter wave measure-

ments on SBN:60 single crystals revealed unexpected behavior which does not fit

accepted models for the dielectric properties. Principally, a high level of

dielectric loss was found in all samples, and relatively large decreases were

noted in permittivity from the low frequency values. Since the envisioned phase

control applications require much lower loss, the source of the observed high

loss and its dependence on controllable factors has become our primary interest.

In the second six months, several SBN:60 single crystal samples grown

from ultra-pure chemicals were characterized from 30 to 40 GHz, and from 90 to

100 GHz. Measurements of polar axis dielectric properties, both above and below

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the Curie point, were made from 30-40 GHz. In addition, measurements on two

ceramic systems, lead potassium lanthanum niobate (PKLN)4 and barium strontium

titanate (BST), were undertaken. These systems possess unusual low frequency

dielectric properties which may provide viable alternatives for achieving phase

control.

1.4 Implications for Further Research

All systems examined to date exhibit high dielectric loss at millimeter

wavelengths, the minimum being tan 61, - 0.03 near 40 GHz for a high purity

SBN:60 sample. The generality of this observation, when coupled with high

sample-to-sample variability, suggests a commonly occurring extrinsic factor,

such as growth defects, as the key element. How the frequency scale for polar-

ization fluctuations is tied to such extrinsic influences remains to he ex-

plored. A systematic study of the influence of defect structure on microwave

dielectric properties of ferroelectrics is probably the most appropriate next

step.

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2.0 TUNGSTEN BRONZE COMPOSITIONS

The goal of the present research program has been to investigate and

develop new classes of ferroelectric materials for millimeter wave device appli-

cations. In seeking new materials that have excellent ferroelectric and

dielectric properties with substantially low dielectric losses at millimeter

wave frequencies, it is important to look for families that originate from high

prototypic symmetry with possibilities for lower temperature ferroelectric-

paraelectric phase transitions. For this reason, the tungsten bronze structural

family is potentially important. The bronze compositions can be represented by

general formulae (AI)4 (A2)2C4Blo0 30 and (A1)4 (A2)2B10030, in which A1 , A2, C and

B are 15-, 12-, 9-, and 6-fold coordinated sites in the structure. Because this

family embraces some 100 or more known compounds and several solid solution sys-

tems, there is a good possibility for obtaining suitable compositions of the

desired ferroelectric and and high frequency dielectric properties. This very

large family of tungsten bronze materials offers a broad range of ferroelectric

properties with the possibility of "fine tuning" the material response by

composition manipulation, and hence is of major interest for potential milli-

meter wave device applications.

Based on our current work, the tungsten bronze family compositions, as

summarized in Table 2.1, can be divided into two subgroups. This classification

has mainly been developed on the basis of their unit cell dimensions, their cry-

stal growth habits and physical properties which include, for example electro-

optic, dielectric and piezoelectric coefficients. Compositions for both of

these subgroups exhibit interesting, and sometimes contrasting properties. For

this work the tetragonal tungsten bronze Srl.xBaxNb 206 (SBN) system has been

selected for millimeter wave study because of its excellent ferroelectric

properties and extensive characterization. Single crystal growth of SBN by the

Czochralski technique has been under development at Rockwell International for

several years, and the growth of high quality, crack-free, large diameter single

crystal material has been highly successful. This tungsten bronze system be-

longs to the class of smaller unit cell compositions, with the crystallographic

c site vacant; hence it is referred to as an "unfilled" bronze structure.

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Table 2.1

Classification of Tungsten Bronze Family

T.B. Compositions with Smaller T.B. Compositions with LargerUnit Cell Dimensions Unit Cell Dimensions

e.g., Srl_xBaxNb206 e.g., Ba6Ti2Nb8O30 , Sr2Ti2Nb8030Sr2KNb5O15 Ba2.xSrxK..yNayNb 5Ol5, etc.

" Crystal Habit is Cylindrical with * Crystal Habit Square with 424 Defined Facets Defined Facets

" High Electro-Optic and Pyro- e High Electro-Optic Coefficientelectric Effects

e Relatively Low Dielectric Constant" High Dielectric Constant

e High Piezoelectric d15 Coefficient" High Piezoelectric d33 Coefficient but Low d33

but Low d159 Moderately Large Crystals are

" Large Crystals with Excellent Available (- 1 - 1.5 cm)Quality are Available (2 - 3.0 cmin Diameter)

Another bronze system, Pbl _2xKx~x3+Nb20 where M = La or Bi, studied2nte 6' eeM=L o 1 tde

in this work is based on the unfilled orthorhombic structure of PbNb206. In

this case the addition of K+ + M3+ ions not only stabilizes the structure by

occupying the 15- and 12-fold coordinated sites, but also enhances the dielec-

tric and piezoelectric properties of this solid solution system. Furthermore,

in the orthorhombic phase this system has a spontaneous polarization with co-

mponents along two crystallographic directions, namely the c- and b-axes, and

this should give rise to interesting behavior in the millimeter wave cross-axis

dielectric sensitivity to an applied electric field.

A discussion of the growth of these bronze compositions and their

structural and ferroelectric properties is given in the following sections.

2.1 Single Crystal Growth of Srl_xBaxNb 206 Compositions

Considerable effort has been made to grow and characterize

Srl-xBaxNb2O6 , x a 0.4 and 0.5, solid solution crystals grown by the Czochralski

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technique.2,5 We have now demonstrated the ability to grow large diameter (2 to

3 cm) SBN:60 and SBN:50 single crystals which show good electrical, mechanical

and optical quality for potential use in a wide variety of applications.

Although the end members SrNb 206 and BaNb 206 do not belong to the tungsten-

bronze structural family, the solid solution Srl-xBaxNb 206 crystallizes in the

tetragonal tungsten bronze structure for 0.25 < x < 0.75.6

Figure 2.1 shows the limit of solid solubility range for the three dif-

ferent phases, e.g., SrNb206 , BaNb 206 and Srl-xBaxNb 206, and the iation of

the ferroelectric phase transition temperature for the tungsten t ize solid

solution. This tungsten bronze solid solution has been shown to .ry useful

for several device applications since it exhibits the largest ele )-optic7 and

pyroelectric coefficients of any well behaved material. 8 Accordi our

current work, this solid solution possesses temperature compensated orienta-

tions6 and should also be useful for millimeter wave applications.

Work by Megumi et al9 indicates that the composition Sro. 6oBao.40Nb206

(SBN:60) is the only congruently melting composition of the entire series. The

Czochralski growth technique has already been established for SBN:60, and cry-

stals as large as one-inch diameter have been developed. This technique has

been applied to other compositions within this solid solution. Although the

composition Sro.5 0Bao.5 0Nb206 is not congruently melting, it exhibits interest-

ing ferroelectric and optical properties; it was selected in the present work to

compare its high frequency dielectric properties to those of SBN:60 and thereby

obtain information on the range of properties available in the SBN system.

Initially, SBN:50 crystals were pulled using SBN:60 crystals as seeds,

and this proved successful in obtaining reasonably large seed material for

subsequent Czochralski growths of this composition. Several fracture-free and

reasonably good quality single crystals of SBN:50 and SBN:60 have now been

successfully grown, with crystal diameters in the range of 1 to 3 cm. These

crystals were pulled along the crystallographic c-axis (001), and although

growths along other orientations such as (100) and (110) have been performed, it

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200

150

r O or- a L BSa';rb2

-- 5 Type-Phase Tur ster ronze Type ,,'e-Pnase

Solid So~uticn

rNb206 0.20 0.40 0.60 0.80 8aX;,C

COMr*PCSITIO; IN I'JLEo

Fig. 2.1 Phase boundary and Curie temperatures vs composition forSr1 -xBaxNb20 6-

7

9L Rockwell InternationalScience Center

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is difficult to obtain reasonable size, good quality crystals in these other

growth directions. A summary of the growth conditions for several SBN crystals

is given in Table 2.2. The use of an automatic diameter control (ADC) system in

our new Czochralski puller has significantly improved the general quality of the

crystals grown, and is now in regular use.

Figures 2.2 and 2.3 show typical c-axis growths for SBN:50 and SBN:60,

respectively. These crystals are usually well faceted, which is unusual for

Czochralski-grown crystals. X-ray diffraction studies show that the crystal

habits are based on 24 faces of four prisms: (110), (120), (100) and (130).

These observations are in excellent agreement with results reported by Dudnik

et al 0 for the SrlixBaxNb206 solid solution single crystals. The idealized

form of the crystal is shown in Fig. 2.4. The crystals are pale yellow to

yellow as grown depending on the crystal diameter. Since the ferroelectric

phase transition temperatures for these compositions are low, in the range of

120% or less, the crystals were cooled with great care to room temperature in

order to minimize the potential for cracking.

Since the SBN solid solution system exists over such a wide composi-

tional range (Fig. 2.1), bulk single crystal growth by the Czochralski technique

can be very difficult. The main problem associated with this technique can be

summarized as crystal diameter instability during growth and thermal cracking.

Inhomogeneity along the growth direction and core causes strain central to the

growth axis, accounts for the presence of striations in the crystals, and may

also affect dielectric losses at both low and high frequencies.

The problem associated with coring has been largely eliminated in

SBN:60 crystals by pulling the crystals at a composition as close to the congru-

ent melt as possible. However, since SBN:50 is not a congruent melting com-

position, the growth of defect-free crystals in this case is much more diffi-

cult, and therefore SBN:50 crystal diameters have been generally confined to

1 am or less. The presence of significant optical striations and high dielec-

tric losses at millimeter wave frequencies (tan 6 > 0.1) in early growths of

these compositions are believed to be due to several experimental factors. Most

authors concerned with the growth of SBN report the existence of striae

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44,

41 - 9 -Ag I I

WW u to X

4A 4.)4.

4A 'AD

o0 C:-- - 0 0. . . . . .

- . - - - - - - -

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or

Fig. 2.2 SBN:50 single crystal grown along the (001) direction.

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L

Fig. 2.3 SBN:60 single crystal grown along the (001) direction.

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(201)

Fig. 2.4 Idealized form of SBN single crystals.

12


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(or refractive index variations) in these crystals. The striae are generally

attributed to variations in the growth temperature causing variations in the

composition, in particular the Sr/Ba ratio. Besides this problem, we suspect

that there are some other problems which are responsible for introducing defects

in SBN single crystals. They are as follows:

a. Reduction of Nb5+ to Nb4+ at the growth temperature (if oxygen

pressure is low). Nb4+ acts as an impurity.

C2+ adF 3+ ntesaigb. Presence of impurities, e.g., Ca and Fe , in the starting

materials. Initially reagent grade chemicals were used in this

work.

c. Temperature fluctuation in our old pulling unit (± 3 - 5C)

responsible for excessive temperature instability.

As mentioned previously, a new Czochralski growth unit with automaticdiameter control (ADC) has been installed and has been in service for the past

six months. The system has been modified to provide further improvement in

temperature stability (t 2C). If necessary, other modifications will be made

in this system to provide even better temperature stability in future growths.

We recently analyzed several crystals which were grown using analar

grade as well as higher purity chemicals, and found that striations are

definitely connected to a nonuniform distribution of impurity ions such as Ca2+,

Fe3+ , Nb4+ and Ir4+ (if an Ir crucible is used). These impurities were found to

be on the order of 80 ppm or higher in concentration (analar grade chemicals),

and greatly affect crystal quality and coloration. For example, Fe3+-containing

crystals are deep yellow in color, while Nb4+- and Ir4+-containing crystals are

purple to coal black in color, depending on the concentration of impurity

ions. The inclusion of Nb4+ , which results from a reduction of Nb5+, has been

eliminated to a large extent by employing an oxygen pressure of two atmospheres

or more. Since the concentration of Fe3+ and Ca2+ is significantly lower in

higher purity starting materials, striations are substantially reduced, but do

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not completely disappear. Based on these observations, it is clear that future

experiments can be redesigned by either improving the temperature stability

during growth and/or by use of still higher purity chemicals. At this stage, it

appears that temperature stability is now a more significant factor and plansare underway to further modify the thermal gradient in and above the crucible.

We believe that if we can succeed in controlling temperature stability to 0.5 -

1.OC or better, it may be possible to significantly improve SBN crystal quality

and further enhance its potential for use in a number of device areas.

2.2 SBN:50 and SBN:60 Characterization

Powder x-ray diffraction measurements for Srl-xBaxNb206 , x = 0.50, 0.40show a room temperature tungsten bronze tetragonal structure, and according to

the structural refinements by Jamieson et a111 for Sro. 75Bao.25 b206 crystals,

this solid solution system belongs to the point group 4 m. Lattice parameter

measurements from x-ray data on ceramic and single crystal samples give values

of a = 12.482A and c = 3.953A for SBN:50, and a = 12.475A and c = 3.941A forSBN:60, in good agreement with the published results of Jamieson. 11

SBN:50 and SBN:60 compositions have been extensively characterized for

their low frequency dielectric, piezoelectric and optical properties. Measure-

ments were made using deposited gold or platinum contacts on the various sample

orientations. Crystal poling along the c-axis was achieved by field-cooling

from slightly above the Curie temperature with an applied field in the range of

6 - 7.5 kV/cm. A summary of these results is given in Table 2.3. These room

temperature data are excellent, making both SBN:50 and SBN:60 of significant

interest for a number of ferroelectric device applications.

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Table 2.3

Physical Properties of SBN

Property SrO 50Bao 50Nb206 SrO . 60Bao. 40Nb206

Curie Temp (°C) 125 72

Dielectric Constant 500 880K33, at 23C

El ectromechani calCoupling

k15 - 0.13k 1 0.137 0.14

k33 0.48 0.47

Piezoelectric StrainCoeff. (1 x 10-12 C/N)

d15 24 31d33 100 130

Electro-OpticCoeff. r33 (m/V) 130 x 10-12 420 x 10- 12

2.3 The Tungsten Bronze Pb K M3+Nb 0 System

J+ -x xx 2 6The PblKXM xNb206 system is based on the orthorhombic tungsten-bronze

PbNb 206 phase, which was the first oxide ferroelectric ever discovered that was

not a perovskite. 12,13 PbNb 206 has been used commercially as a piezoelectric

ceramic transducer. Its outstanding features are its ability to withstand expo-

sure to temperatures approaching its Curie point (560*C) without severe depol-

ing, its large d33/d31 ratio, and its extremely low mechanical Q. Above the

Curie point, the structure is tetragonal with lattice constants, a = 12.56 and

c - 3.925A, space group P4/mbm, isostructural with potassium tungsten bronze.

Below the Curie point, there is slight orthorhombic distortion, quadrupling the

cell size, with lattice constants becoming a - 17.63, b * 17.93 and c = 7.736A,

space group Cm2.

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Although the Curie temperature was much higher than that of any known

ferroelectric, the material did not find immediate application because of the

difficulty in preparing good nonporous ceramics and the associated problem of

poling them. By analogy with previous work on barium titanate and other ferro-

electric hosts, the effect of replacing part of Pb2+ by other divalent and tri-

valent ions, or Nb5+ by tetravalent or hexavalent ions was studied, 1 4 2 4 with

the objective of improving the sintering and general ferroelectric properties of

the ceramic. It was observed that the Curie temperature decreased, and although

this would be an disadvantage, this made it possible to pole the material more

effectively and successfully enhance the dielectric and piezoelectric proper-3+ties. The systems Pbl_2xKxMx Nb206 , M = La or Bi, and Pbl_xBaxNb 206 are typical

examples of such substitutions. Their dielectric and piezoelectric properties

are excellent and they are promising candidates for high frequency dielectric

studies.

Sc 3+Since Pb.1 2xKxMx Nb2 06 is a relatively new tungsten bronze system, and

furthermore, since single crystal growth of lead-containing oxides is very dif-ficult due to lead volatilization at the melt temperature, the work on this sys-

tem for this program has been confined to sintered ceramic samples. PbO, K2CO3

(Baker Analyzed Grade), Bi2O3 (Fisher Scientific Co.), La203 (American Potach

and Chem. Corp.), and Nb205 (Atomergic Co.) were used as the starting materials.

The ceramic specimens were prepared by the conventional technique of milling,

prefiring, crushing, pressing and firing. The specimens were prepared in the

form of disks 1.3 cm in diameter and 0.3 cm thick. The final sintering was for

2 - 3 hr, and the temperature, which depended on composition, was between 12500

- 1300C.

The work on Ko. 5Lao.50 Nb206 by Soboleva et al. 2 5 and our work on

Ko.5Bio. 5Nb206 show that these two phases crystallize in the tetragonal crystal

symmetry and are isostructural with the high temperature tetragonal modification

of PbTa206. At room temperature, the ferroelectric PbTa206 phase has an ortho-

rhombic symmetry and is isostructural with the tungsten bronze PbNb 206 phase.

This suggests that all the systems considered in this work are structurally re-

lated and should form a continuous solid solution in the pseudo-binary systems

PbNb 206 -Ko. 5 Lao.5 Nb20 6 and PbNb206-Ko.5Bio.5 Nb206. The results of x-ray dif-

16i C5278A/Jbs


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fraction powder work are in good agreement, and a complete solid solution has

been identified in both of the systems. Three structural related phases,

namely, the orthorhombic and the tetreagonal tungsten bronze type phases and the

tetragonal Ko.05La0 .5Nb206 , have been established for the Pb. 2 K M3+Nb206, M =

La or Bi, solid solution system.

The results of x-ray measurements at room temperature show a homogene-

ity range of the orthorhombic tungsten bronze phase to x = 0.47, while the

tetragonal tungsten bronze phase is present in the composition range 0.48 > x

0.85. At the other end, the crystalline solid solubility of PbNb 206 in the3+Ko. 5M0 .5Nb206 phase is limited and is estimated to be in the composition range

0.86 x > 1.0. At composition x = 0.47, both the orthorhombic and tetragonal

tungsten bronze phases coexist. This type of morphotropic condition has also

been reported on the Pbl-xBaxNb 206 system.14 ,2 1 The variation of lattice

parameters as a function of composition for the system Pbl_ 2xKxLaxNb2O6 is shown

in Fig. 2.5. The a and c parameters increase only slightly, while the b3+L

parameter decreases considerably with increasing concentration of K0 .5 O.5Nb 2O6

in the PbNb206 phase. The decrease in the b parameter is substantial compared

to the a parameter, so that the ratio b/a becomes close to unity for values

x 4 0.50.

2.4 PKLN/PKBN Characterization

A typical plot of the low frequency (10 kHz) dielectric constant vs

temperature is given in Fig. 2.6 for a few compositions in the Pbl_ 2xKxLaxNb2O6

system. It can be seen that the dielectric constant decreases and broadens

whereas the room temperature dielectric constant increases with increasing K+

and La3+ or B13+ up to x = 0.40. Furthermore, the ferroelectric phase transi-

tion temperature Tc is shifted towards a lower temperature with increasing

amounts of Ko.sLao.0Nb206 in PbNb206- Tc for the pure PbNb206 has been recorded

at 5600C, and this temperature drops with the addition of K+ and La3+ or B13+ in

both the orthorhombic and the tetragonal tungsten bronze phases. By using this

peak position, the transition temperature for each system has been determined.

Figure 2.7 shows the variation of the Curie temperature of Tc as a function of

composition for the Pbl.2xKxLaxNb2O6 and Pbl. 2xKxBixNb2O6 systems. Variation

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395 MRDC81-12758

2 3.85 11

31.90

Z17.805

217.70 p oUNIT CELLabAo

ORURHMI I TETRGONA

17.88

. -j .. - .a

OD Rockwell InternationalScience Center

5C5344.7FR

SC82-1 7598

II3500 - A: Pb0 ~rjK0 0 5La0 .0 5Nb2 O6

89: Pb0.80 K0 1 0 La0 .j0 Nb2O6 BC: PbO.7 0K01j5 La0 .j5 Nb2O6D: Pb0.60 K0 .20 Lam2 0Nb2O6

3000

A

2500

o 2000

LULU

1000

500

0 100 200 400 400 500 600TEMPERATURE (0C)

Fig. 2.6 Dielectric constant vs temperature of Pbi..2xKxLaxNb206.

19 ________

IF:

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Soo SC82-17599

A: Pbl_2xKxLaxNb 2 O6

B: Pbl_2xKxBixNb206

400-

'U I200 I I

A \ PARAELECTRICTETRAGONAL

'U ORTHORHOMBIC TETRA.I-w2 (FERROELECTRIC) - (PARA)

I \ I-200 -TETRAGONAL-

(FERROELECTRIC)

,III I

PbNb206 0.2 0.4 0.6 0.8 K0 .5 M0 .5Nb 2O6

COMPOSITION. MOLE %

Fig. 2.7 Variation of the ferroelectric transition temperature forPbl_2xKxMxNb 206, M = La or Bi.

20

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of Tc with composition is linear in both systems and is approximately of the

same order. Lowering of Tc has also been reported for several other systems

based on PbNb 206 solid solutions.15 ,18 -2 3

The effect of a variety of different substituent ions, such as Ba

Sr2+, Ca2+, Cd2+ and Bi3+ for Pb in the PbNb 206 phase, has been studied and

reported in literature. 14 "2 4 Except for Ba2+, all other ions are smaller than

Pb2+ , and their addition did not alter the orthorhombic crystal symmetry.

However, in the case of the Pbl_xBaxNb 206 solid solution system, the substi-

tution of Ba2+ (1.50A) for Pb2 + (1.32A) first decreases the orthorhombic dis-

tortion, and then induces a tetragonal structure with the polar axis along the c

rather than along the b axis. Further, the interesting feature in this system

is that Tc first decreases in the orthorhombic tungsten bronze phase and then

increases in the tetragonal tungsten bronze phase. This is the unique case in

the PbNb206 based solid solutions; also, since the average ionic size of K+ +

La3+ (1.355A) and K+ + Bi3+ (1.34A) is bigger than Pb2+ , and since both

systems, Pb26 M = La or Bi, and Pbl-xBaxNb206 , are structurally

similar, it was expected that the addition of K+ with La3 + or Bi3+ would produce

similar results, i.e., first a decrease and then an increase in Tc.

However, the results of this work (Fig. 2.7) indicate that a continu-

ously decreasing Curie temperature occurs with increasing amounts of K+ + La3+

or K+ + Bi3+ in both the orthorhomic and tetragonal tunsten substitutional

bronze phases, indicating that Tc is not only controlled by the size of substi-

tuent ions, but its location in the structure is equally important. Since the

coordination of Pb2+ is 15- and 12-fold in the tungsten bronze structure, there

exists three possibilities for each ion in this structure, namely in the 15 or

12, or in both sites. Neither the work reported in the literature 14 -20 nor the

results of this investigation are sufficient to establish the site preference or

their distirbution over the two crystallographic sites. Further work in this

direction is of significant interest in order to establish the site preferences

for differnt ions and their influence over the behavior of the Curie temperature

and the ferroelectric and millimeter wave dielectric properties.

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Figure 2.8 shows the variation of the low frequency dielectric constant

(at Tc and at room temperature) and the room temperature dielectric losses as a

function of the sintering temperature for the Pbo.8Ko. 1Lao. 1Nb206 composition.

Data for other compositions are similar to that shown in Fig. 2.8. In general,

the sintering temperature was held below 1290°C to avoid softening of the disks;

soak time was 2 - 3 hours, with no significant improvement in the dielectric

properties with longer times.

Table 2.4 summarizes the physical constants for the Pbl_2xKxLaxNb 206

(PKLN) and Pbl_ 2xKxBixNb2O6 (PKBN) systems. As can be seen from these data, the

dielectric constant has increases significantly with the addition of K+ and La3 +

or Bi3+ in the orthorhombic tungsten bronze phase with the compositions

Pbo.8 Ko. 1Lao.1 Nb206 (PKLN 80/20) and Pbo. 7Ko. 15Bio.15Nb 206 (PKBN 70/30) exhibi-

ting the optimum dielectric constant for each system. The piezoelectric strain

coefficient (d33 ) measurements on various samples were performed using the

Berlincourt d33- meter and the results of this study indicate that the composi-

tion Pbo. 8Ko. 1Lao. 1Nb2O6 again shows the optimum d33 coefficient for these sys-

tems. We believe these values may increase substantially if the poling is

achieved at higher temperatures. In the present case, poling was accomplished

in a silicon oil bath at approximately 150°C, which is a very low temperature

compared to the respective Curie temperatures. It is anticipated that by im-

proving the poling technique for these ceramic samples it will be possible to

better establish the d33 coefficient. In any case, the present piezoelectric

strain coefficient value obtained for the Pbo.8 Ko. 1Lao.1Nb206 sample is much

higher than that reported for the PbNb 206 crystal, indicating that these com-

positions can find use for piezoelectric transducer and high frequency dielec-

tric applications. However, the results for the Pbl_ 2 xKxBixNb206 compositions,

although quite good, are not as good as those for the best of the

Pb1_2xKxLaxNb206 compositions. Furthermore, many of the PKBN samples proved to

be difficult to pole; hence, for this study our work has focussed on composi-

tions from the Pb1_ 2 xKxLaxNb2O6 system for millimeter wave dielectric

characterization.

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230C

0.8 eEEmax

0.6-

0.4- 1 kHz

tan 6 (x10)

0.1270 1280 1290 1300

SINTERING TEMP, 0CFig. 2.8 tper2 a ureb206 dielectric properties as a fUnction of sintering

23


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Table 2.4

Physical Constants for Modified PbNb206

DielectricCurie Constant, K Piezoelectric

Temperature Strain Coeff.,Composition* Tc, °C R.T. Tc d3 3 c/n

PbNb206 560 100 10-12

Pbo.90 Ko.0 0 La0 .0 5Nb 206 455 288 2610

Pbo.80 Ko.1 oLaO.lONb20 6 339 720 3390 130 10-12

Pbo.70 Ko.15La0 .15Nb 206 201 790 1600 106 10-12

Pbo.60 Ko.2oLao.2oNb 206 98 650 830 ---

Pbo.80 Ko.10Bio.1 0Nb206 342 280 2310 30 10- 1 2

Pbo.70K0 .15Bo.15Nb 206 211 750 2840 35 10- 12

Pbo.60Ko.20Bio.2Nb 206 105 1390 2380

*All compositions are orthorhombic.

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3.0 HIGH FREQUENCY DIELECTRIC MEASUREMENTS

The primary objective of this contract effort has been to determine the

feasibility of using the electric-field sensitivity of the microwave refractive

index in available ferroelectrics as a means to control the phase of a trans-

mitted millimeter wave radar beam. Using SBN:60 crystals grown in this labora-

tory, we had observed sensitivities dn/dE of the order of 10-6 meters/volt.1

For the beam-steering application we envisioned, this sensitivity would require

AC voltages around 2000 volts; an improvement to 10-5 meters/volt or higher was

deemed necessary for implementation with currently avialable solid-state tech-

nology. Within the SBN family order-of-magnitude variations are observed in the

electro-optic coefficients and other related properties, so it is reasonable to

expect that dn/dE may attain much higher values in some of these materials. For

more conventional waveguide phase shifters the measured sensitivity was already

high enough.

A serious and unexpected limiting factor for all applications was

discovered early in the contract effort: millimeter wave losses in the available

ferroelectrics typically exceeded 20 dB per millimeter. To use such a material

in the beam-steering application, an unrealistically thin phase-shifting layer,

less than 50 microns, would be required in order to hold transmission losses to

tolerable levels. The phase shifting electric field in such a layer would reach

tens of kilovolts per centimeter, large enough to depole the film and destroy

the basic effect.

The material factors which cause these large losses are not yet known.

Based purely upon extrapolation from the low freuqency dielectric properties,

one predicts losses in the neighborhood of I - 2 dB per millimeter until fre-

quencies of several hundred gigaherz or temperatures a few degrees below the

ferroelectric-paraelectric transition temperature are reached. We have investi-

gated impurites, compositional fluctuations, and growth defects as possible

sources for the observed high loss. However, as of this writing, no definite

trends have been identified. Under separate contract with the Office of Naval

Research, we are continuing to explore this phenomenon as part of a general

study of millimeter wave properties of high dielectric constant materials.

25

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For this final report, we have carried out measurements of dn/dE in

SBN:60 and SBN:50 at frequencies between 30 and 40 GHz. Although the problem of

high loss at present prevents attainment of the original goal, it is worthwhile

to confirm our earlier measurements, and to establish the trend of values for

dn/dE within the SBN solid solution system.

3.1 Measurements of dn/dE

The method of measurement is a straightforward application of transmis-

sion modulation similar to that described by Boyd et al. ( ) In thois technique,

a properly oriented and poled sample in waveguide is subjected to a transverse

low-frequency electric field, and the resulting modulation in transmitted power

is synchronously detected.

Results of these measurements for SBN:60 are typified by the linear

response illustrated in Fig. 3.1. In this figure, the left-hand axis compares

the power variation in the modulated signal to the transmitted power in the

absence of an applied field, while the right hand axis displays the change in

permittivity required to produce the observed modulation. Sample thickness in

this case was 1.12 millimeters. From the variation of permittivity with applied

field, one calculates a value for the c-axis sensitivity dn33/dE3 of (5.83 1

0.14) x 10- 7 meters/Volt at 33 GHz. This is about a factor of two smaller than

the value obtained in our earlier work at 58 GHz. The equivalent electro-optic

coefficient r33 = 2 n-3 dn/dE in this sample is 3.8 x 10-10 meters/Volt. The

frequency dependence of dn/dE for this sample was not large, but showed an

increasing trend from 30 to 35 GHz, reaching values of 7 x 10- 7 meters/Volt at

the high end.

A similar series of measurements on SBN:50 gave the results summarized in

Table 3.1. Here one sees a steady decrease in dn33/dE3 between 33 and 37 GHz,from 5 x 10- 7 to 1.5 x 10- 7 meters/Volt. In view of the large sample-to-sample

variability in millimeter wave dielectric properties which we have found in

these materials, one should be cautious in drawing any general inferences from

the trends in these data. At most, one can note that SBN:60 and SBN:50 samples

showed sensitivities of the same order, closely paralleling the electro-optic

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response reported for these materials. These values may be compared with the

low-frequency values of d(We33 )/dE3, which for SBN:60 is about 2 x 10-6 meters/

Volt at room temperature.

Table 3.1

Variations of dn/dE with Frequency and Applied Voltage for SBN:50

AT2(.)/To2 V dn/dE

33 GHz 0.00505 65 5.054 x 10-7

0.00962 120 5.214 x 10-7

0.0171 215 5.173 x 10-7

0.0228 300 4.943 x 10-7

0.0339 400 5.513 x 10-7

0.0362 480 4.906 x 10- 7

0.0472 640 4.797 x 10-70.0538 736 4.755 x 10-7

35 GHz 0.0041 60 3.619 x 10-7

0.00871 120 3.844 x 10- 7

0.0142 205 3.688 x 10-7

0.0228 315 3.833 x 10-7

0.0273 400 3.615 x 10"_0.0373 512 3.858 x 10- 7

0.0494 736 3.555 x 10-7

37 GHz 0.00219 70 1.71 x 10- 7

0.00459 120 2.10 x 10- 7

0.00688 200 1.88 x 10 7

0.00940 350 1.47 x 10- 7

0.0115 400 1.58 x 10-70.00757 275 1.51 x 10"_0.0135 528 1.40 x 10-70.0187 736 1.39 x 10"-

3.2 Dielectric Studies

The bulk of our dielectric measurements at millimeter wavelengths have

been summarized in previous contact reports. However, the data supporting

certain of our conclusions have not been presented in detail. In this section,

measurements are reported on several different SBN samples, prepared under a

range of conditions, and the inferences we have drawn from these data are stated

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once again. Also, the results from a limited number of millimeter wave mea-

surements on lead potassium lanthanium niobate (PKLN) ceramics are presented.

From a theoretical viewpoint the effects of poling on millimeter wave

dielectric properties of SBN should be very small. To check this, two c-axis

samples from the same growth were measured from 30 to 40 GHz before and after a

thorough poling. One of these samples (see Table 3.2 below) turned out to have

the lowest values for E33 found under this program: c = 36 + 112, while the

other showed a more typical range around c = 135 + 160. As can be seen from the

Table, neither sample was much affected by the poling. Quite possibly, the

details of sample fit in the waveguide are responsible for the observed differ-

ences. By far the most significant fact is the radical difference in c betweenthe two samples, which forces us to conclude that extrinsic factors varying

during growth can swing the millimeter wave dielectric properties over a wide

range. It should be noted that no comparable variations in the low frequency

permittivity among poled samples has been found.

The possibility that growth striations, corresponding to small periodic

fluctuations in crystal composition, could be responsible for the high observed

losses was tested by annealing out all visible striations on three samples from

a recent growth. Dielectric data on these samples, summarized in Table 3.3,

show that losses are at least as large as in striated samples.

Minimizing the effect of impurities on the loss was attempted in growth

number 112, which used ultra-pure starting materials. In this case, three sam-

ples were characterized between 90 and 100 GHz and two were measured between 30

and 40 GHz. The dielectric properties for these samples are given in Table 3.4.

Once again, no significant effect on loss is seen: tan 6 ranges from 0.1 to 0.7.Also, the sample-to-sample variability in dielectric properties stands out

clearly, with c' differing by a factor of two between the low-frequency samples,

and by a factor of three between the two high-frequency a-axis samples.

Given this wide scatter in results, one must seriously consider the

possibility that there is a hidden defect in the measurement method itself. To

check the method, a high purity, high dielectric constant, single crystal of

T1O 2 was obtained from Penn State and cut into appropriately dimensioned

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Table 3.2

Dielectric Properties of Two SBN:60 Samples Before and After Poling

Before After

F(GHz) R2 T2 (x 10-2) E R2 T2 (x 10-2)

Sample #1Thickness = 0.874 mm

31 0.631 2.34 35.4 + 116.3 0.625 2.51 35.5 + 115.732 0.631 2.75 36.7 + 114.7 0.620 2.93 36.4 + 114.233 0.654 3.16 38.1 + 112.8 0.622 3.18 36.1 + 113.434 0.661 3.30 37.6 + 112.2 0.640 3.25 36.3 + 112.835 0.672 3.55 37.2 + 111.1 0.654 3.38 36.2 + 112.036 0.678 3.89 36.3 + 110.1 0.666 3.48 35.8 + 11.437 0.679 4.13 35.2 + 19.5 0.669 3.72 35.0 + 110.538 0.683 4.49 34.2 + i8.7 0.671 3.86 34.2 + i10.0

Sample #2Thickness = 0.907 mm

31 0.843 0.90 136 + 178 0.829 0.775 110 + i6832 0.835 1.11 136 + i63 0.822 0.702 114 + i7033 0.834 1.38 139 + 159 0.824 0.732 125 + 17034 0.831 1.71 142 + 155 0.825 0.899 135 + 16735 0.828 2.14 145 + i55 0.821 1.09 137 + 16336 0.827 2.51 139 + i47 0.813 1.47 137 + i5737 0.822 3.16 136 + 143 0.817 1.91 139 + i5238 0.821 3.52 127 + 140 0.813 2.37 130 + i47

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Table 3.3

Dielectric Properties of Three Annealed SBN:60 Samples

C-axis

Sample #1 - Thickness = 0.376 mm Sample #2 - Thickness = 0.419 mm

F(GHz) R2 T2 (x 10- 3 ) R2 T2 (x 10- 3 )

31 0.868 1.9 216 + 1135 0.891 1.4 226 + 113033 0.834 3.2 186 + 1112 0.864 1.9 191 + 111835 0.830 3.7 186 + 1102 0.845 2.9 171 + 19837 0.808 5.3 166 + i86 0.812 4.7 146 + i7839 0.803 6.3 156 + i76 0.803 6.0 136 + 168

A-axisThickness = 0.434 mm

F (GHz) R2 T2 (x 10-3 ) E

31 0.911 2.2 246 + 19233 0.830 6.5 161 + 16335 0.724 19.3 121 + 14037 0.745 26.8 121 + 12639 0.777 26.8 116 + i23

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Table 3.4

Dielectric Properties of High Purity SBN:60 Samples

C-axis, 30 - 40 GHz


F(GHz) R2 T2 (x 10- 3 ) C R2 T2 (x 10-3) C

30 0.871 1.26 150 + 1112 0.912 0.18 285 + 123733 0.828 3.16 133 + i81 0.871 1.00 185 + 113136 0.782 8.91 112 + 150 0.851 2.51 225 + i9939 0.785 10.0 106 + 144 0.822 5.62 205 + 169

A-axis, 90 - 100 GHz


92 0.871 2.00 245 + i76 0.708 6.31 65 + 11794 0.841 2.51 215 + 172 0.776 5.62 79 + 11796 0.822 2.24 190 + 176 0.759 5.01 75 + i1898 0.822 2.37 190 + 73 0.759 5.01 75 + 118

C-axis, 90 - 100 GHz

Thickness = 0.457 mm

F (GHz) R2 T2 (z 10- 3 )

91 0.794 10.1 131 + i1893 0.794 7.94 127 + 12195 0.794 8.32 124 + 12097 0.794 10.0 120 + 11899 0.794 10.0 117 + 117

samples for measurement at 30 - 40 and 90 - 100 GHz. The results of the mea-

surements are shown in Table 3.5. Values derived from the permittivity along

the two principal directions show good internal consistency when samples of

different thickness are used, and they are generally in agreement with low

frequency data on this material. There is some indication of a decrease in the

larger permittivity at 90 GHz, which may be an artifact of the method. Good

sample fit in the waveguide is much more critical at short wavelengths.

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Table 3.5

Summary of Measured Dielectric Properties of Single Crystal T1O 2

Sample No. Thickness (cm) Frequency (GHz) Loss Tangent

Electric Field Parallel to Crystal C-axis

1 0.1062 34.41 152.6 0.00082 0.1011 36.18 151.7 0.0006

1 + 2 0.2073 35.11 153.3 0.0009a 0.098 94.86 131.2 0.0066

Electric Field Perpendicular to Crystal C-axis

1 0.0991 33.85 80.49 0.00032 0.1052 32.08 79.58 0.00043 0.1047 32.22 79.67 0.0004

1 + 2 + 3 0.309 32.87 79.0437.66 81.80 0.0004

a 0.105 93.70 81.62 0.0018

Our dielectric measurements on the PKLN solid solution system have been

confined to two compositions that are orthorhombic (and ferroelectric) at room

temperature. Ceramic samples fabricated by hot pressing were measured from 30

to 40 GHz with the microwave electric field both parallel and perpendicular to

the pressing axis. Dielectric data for these samples are presented in Table 3.6.

Both c' and tan 6 are found to be similar in magnitude to those seen in the

poorest SBN:60. Permittivities along the pressing axis are somewhat higher than

those measured perpendicular to the axis.

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Table 3.6

Dielectric Properties of Orthorhombic PKLN Samples

Pbo 7Ko. 15La0 15Nb206

Parallel to axis - Perpendicular to axis -

thickness = 0.93 mm thickness = 0.91 mm

F(GHz) R2 T2 (x 10- 3) R2 T2 (x 10- 3 ) e

31 0.820 2.51 122 + 147 0.785 2.75 49 + 13733 0.794 2.51 108 + i47 0.767 2.75 58 + i3835 0.794 1.70 108 + 151 0.755 2.14 73 + i4637 0.766 1.20 91 + 153 0.746 1.58 79 + i4939 0.714 1.41 59 + i44 0.736 1.26 75 + i50

Pbo 8Ko iLao 1 Nb206

Parallel to axis - Perpendicular to axis -

thickness = 0.96 mm thickness = 0.96 mm

31 0.822 3.16 120 + i41 0.813 2.00 110 + 14833 0.817 1.82 118 + i50 0.794 1.45 99 + i5235 0.820 1.00 146 + i63 0.794 0.71 102 + i6237 0.804 0.40 142 + i76 0.762 --39 0.794 0.32 138 + 177 0.700 ..

*Loss measurements indeterminate due to standing wave interference.

I.

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4.0 CONCLUSIONS

4.1 A major success of this contract effort has been development of the

Czochralski growth technique for the tungsten bronze family ferroelec-

trics, specifically SBN:50 and SBN:60 compositions. Although SBN:50 is

not a congruent melting composition in this system, our technique

yields high quality crystals of 2 cm in diameter for this composition.

4.2 Low frequency dielectric properties of both compositions have been

evaluated and they show low loss and high permittivity as expected.

However, high frequency properties of these materials are significantly

different. In particular, losses at millimeter wavelengths are very

high, in excess of 20 dB/mm. Such losses would appear to rule out the

device applications originally envisioned to utilize the large non-

linear dielectric response. Our measurements of this response confirms

that values of dn/dE of the order 10-6 m/V are achieved in this solid

solution system.

The current observations suggest that these losses are con-

nected to extrinsic factors acting during crystal growth and also to

the distribution of Ba2+ and Sr2 + over the two 15- and 12-fold cry-

stal' graphic sites in the tungsten bronze structure. Future work

should concentrate on the influence of environmental factors such as

temperature and pressure both during and after crystal growth. Such

conditions should also be varied systematically during high frequency

measurements.

4.3 In the course of this program, a variety of other ferroelectrics have

been examined in ceramic form, e.g., PLZT, PZT, PKLN, PBN, PST etc. In

general, the losses are substantially higher in these ceramic

materials. We believe the other ferroelectrics such as Gd3 (Mo04 )3(GMO) and Bi4Ti3O12 should be tried at millimeter wave frequencies.

These crystals exhibit more than one polar direction, so that large

anisotropic effects can be induced in these materials.

34. .. 52 .. I I-

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5.0 PUBLICATIONS AND PRESENTATIONS

5.1 Publications

1. R.R. Neurgaonkar, W.K. Cory, W.W. Ho, W.F. Hall and L.E. Cross,

"Tungsten-Bronze Family Crystals for Acoustical and Dialectric

Applications," Ferroelectrics 38, 857, (1981).

2. W.W. Ho, W.F. Hall, R.R. Neurgaonkar, R.E. DeWames and T.C. Lim,"Microwave Dielectric Properties of Sro. 61Bao. 39Nb2O6 Single

Crystals at 35 and 58 GHz," Ferroelectrics 38, 833, (1981).

3. R.R. Neurgaonkar, J.R. Oliver, W.K. Cory and L.E. Cross, "Struc-

tural and Dielectric Properties of the Phase Pbl_ 2KxM3+Nb 2O6,Phase, M = La or Bi," Mat. Res. Bull. 18, 735, (1983).

5.2 Presentations


"Tungsten-Bronze Family Crystals for Acoustical and DielectricApplications," presented at the 5th Int. Meeting on

Ferroelectricity, Penn State Univ., PA, August 17-21, 1981.

2. W.W. Ho, W.F. Hall, R.R. Neurgaonkar, R.E. DeWames and T.C. Lim,

"Microwave Dielectric Properties of Sro. 61Bao. 39Nb2O6 Single

Crystals at 35 and 58 GHz," presented at the 5th Int. Meeting ofFerroelectricity at Penn State Univ., PA, August 17-21, 1981.

35 C5278A/Ibs...

Q % Rockwell InternationalScience Center

SC5344 .7FR

6.0 REFERENCES

1. R.E. DeWames, W.W. Ho, W.F. Hall, R.R. Neurgaonkar, and T.C. Limn, Bull.

APS 26, 303, 1981.

2. R.R. Neurgaonkar, M.H. Kalisher, T.C. Limi, E.J. Staples and K.L. Keester,

Mat. Res. Bull. 15, 1235 (1980).

3. W.W. Ho, W.F. Hall, R.R. Neurgaonkar, R.E. DeWames and T.C. LimT,

Ferroelectrics 38, 833 (1981).

4. R.R. Neurgaonkar, J.R. Oliver, W.K. Cory and L.E. Cross, Mat. Res. Bull.

18, 735 (1983).

5. A.A. Ballman and H. Brown, J. Cryst. Growth 1, 331 (1967).


Ferroelectrics 38, 857 (1981).

7. P.L. Lenzo, E.G. Spencer and A.A. Ballnian, Appl. Phys. Lett. 11, 23

(1976).

8. A.M4. Glass, J. Appi. Phys. 40, 4699 (1969).

9. K. Megutni, N. Nagatsuma, Y. Kashiwada and Y. Furuhata, J. Mat. Sci. 11,

1583 (1976).

10. 0.F. Dudnik, A.K. Groniov, U.B. Kravchenko, Y.L. Kopylov and G.F.

Kunznetsov, Sov. Phys. Cryst. 15, 330 (1970).

11. P.B. Jamieson, S.C. Abrahams and J.L. Bernstein, J. Chemi. Phys. 48, 5048

(1968).

36C5278A/Jbs


SC5344. 7FR

12. G. Goodman, Am. Cer. Soc. Bull. 31, 113 (1952).

13. G. Goodman, Au,. Cer. Soc. Bull. 36, 368 (1953).

14. M.H. Francombe, Acta. Cryst. 13, 131 (1960).

15. V.A. Isupov, V.I. Koiakov, Zh. Tekh. Fiz. 28, 2175 (1958).

16. E.G. Bonnikova, I.M. Larionov, N.D. Smazhevskaya and E.G. Glozman, lzv.

Akad. Nauk. SSR., Ser. Fiz. 24, 1440 (1960).

17. B. Lewis and L.A. Thomas, Proc. Int'l. Conf. Solid State Phys.

Electronics Telecommun., Brussel 4, Pt. 2, 883 (1960).

18. G. Goodman, Am. Ceram. Soc. Bull. 34, No. 4, Program 11 (1955); U.S.Patent 2,805,165, Sept. 3, 1975, filed April 25, 1955.

19. G. Goodman, U.S. Patent 2,729,757, June 3, 1956; filed June 29, 1951.

20. P. Baxter and N.J. Hellicar, J. Am. Ceram. Soc. 43, 578 (1960).

21. E.C. Subbarao, G. Shirane and F. Jona, Acta. Cryst. 13, 226 (1960).

22. E.C. Subbarao, J. Amn. Ceram. Soc. 43, 439 (1960).

23. E.C. Subbarao and J. Hrlzo, J. Am. Ceram. Soc. 45, 528 (1962).

24. E.C. Subbarao and G. Shirane, J. Chem. Phys. 32, 1846 (1960).

25. L.V. Soboleva and F.I. Dmltrieva, Inorg. Mat. 6, 1761 (1970).

37C5278A/Jbs

DE .FILE 84 - apps.dtic.mil · date of Sro.61Bao.39Nb206, the congruently melting composition.2...

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Transcript of DE .FILE 84 - apps.dtic.mil · date of Sro.61Bao.39Nb206, the congruently melting composition.2...